1. Field of the Invention
This invention relates to a flash output control failure warning device of an automatic flash output control speed light.
2. Description of the Prior Art
A typical serial control type automatic flash output control speed light includes a main discharge tube adapted to consume the charge stored in a main discharge capacitor and emit flashlight, a light-receiving element for receiving the reflection of the light emitted from the main discharge tube by an object and decreasing the resistance value thereof, and a thyristor (SCR) disposed in the discharge path between the main discharge tube and the main discharge capacitor, and is designed such that when the integrated value of the current flowing to the light-receiving element reaches a predetermined value, the thyristor is turned off to prevent the discharge of the main discharge capacitor, thereby discontinuing the light emission of the main discharge tube. That is, by controlling the light emission time of the main discharge tube, the quantity of light emitted therefrom is controlled. However, when an object to be phototaken lies at a relatively far distance, the reflection of the light emitted from the main discharge tube by the object is small and accordingly, the operation of the main discharge tube terminates before a desired quantity of emitted light is obtained. In other words, before the integrated value of the current flowing to the light-receiving element reaches a predetermined value, the operation of the main discharge tube terminates and the flash output control operation is not effected and results in a failure. In such a case, there has been a disadvantage that the erroneous photography resulting from an under-exposure cannot be discovered until film is developed, because the conventional automatic flash output control speed light does not have the function of confirming the flash output control operation. Accordingly, if the function of confirming the flash output control operation could be given to an automatic flash output control speed light, it would become possible to discover erroneous photography and the usefulness of the automatic flash output control speed light would be greatly enhanced. This also holds true of a parallel control type automatic flash output control speed light. Techniques which enable, when it is detected that the thyristor has been turned off (or that the integrated value of the photocurrent has reached a predetermined value), the display of the fact that the flash output control operation has been effected, namely, that the flash output control has been successful have been proposed by U.S. Pat. Nos. 3,706,911 and 3,999,193.
However, usually, failure of automatic flash output control occurs very rarely as compared with success of automatic flash output control and therefore, the system of displaying success of automatic flash output control as has heretofore been done is rather onerous to the photographer. Also, what is important to the photographer is to know a failure rather than a success. Accordingly, a warning device which positively calls the photographer's attention during failure of automatic flash output control photography would be desirable.